The present invention relates to an optical pickup.
An optical pickup, for reading/recording information from/onto an optical disc, is sometimes heated up to high temperature, due to large consumption of electric power within a semiconductor and/or a laser driver circuit. For this reason, it is necessary to increase the heat radiation performance or capacity, in particular, of the semiconductor laser and the laser driver circuit, and such a design is made that the temperature will not exceed a guaranteed temperature of that part(s).
In recent years, because of demands made upon light weighting and/or low costing of the optical pickup, it is desired to manufacture a housing of the optical pickup, conventionally being made from a metal die-cast, of a resin. However, applying the resin, being low in the heat conductivity comparing to the metal, causes a problem of lowering the heat radiation performance or capacity of the semiconductor laser.
With a housing of the optical pickup made of resin, conventionally, the heat radiation performance or capacity for the semiconductor laser is maintained by connecting a metal-made bottom cover with the semiconductor laser, thermally, but a heating value (i.e., an amount of heat generation) of the semiconductor laser also goes up to be large accompanying with an increase of an output of the semiconductor laser; therefore it is in such a situation that sufficient performance or capacity of heat radiation cannot be obtained, by means of such conventional bottom cover.
In the following Patent Document 1, for the purpose of increasing the heat radiation capacity of that bottom cover, there are disclosed a shaft, for supporting the optical pickup to be movable in a radial direction of an optical disc, and also the structures to be thermally connected with an end of the bottom cover.
And the optical pickups can be classified, roughly, into the followings; i.e., a thin-type one, which is suitably applied into an optical disc drive for use in a note-type personal computer, and a large-size one for an optical disc drive, which is mainly applied into a DVD recorder or a desktop personal computer, etc. The thin-type optical pickup has thickness less than 10 mm, mounting a driver equipment or mechanism for an objective lens within an inside of the housing of the optical pickup, and has such the structures that metal members for supporting a magnet can expose into an outside from a bottom cover side; i.e., an opposite side of a surface of the housing of the optical pickup facing to the optical disc.
On the other hand, the large-size optical pickup has thickness equal or greater than 10 mm, mounting the driver mechanism for the objective lens on the surface of the housing of the optical pickup, but facing to the optical disc, and it has such the structures that the metal members for supporting the magnet cannot expose outside into the side of the bottom cover.
In the driver mechanism for the objective lens, the objective lens, on which a coil is attached, is supported in space through elastic forces of wires. Through the wires can run current into the coil, and due to electromagnetic force generated by the coil accompanying with this and that of the magnet, the objective lens is driven. The heat generated in the coil attached on the objective lens can radiate into an air surrounding the coil, but because a gap defined between the magnet and the coil is very small, then almost of the heat transmitting to the air transfers to the magnet, so that it increases the temperature of the magnet.
Within the metal housing of the optical pickup of the conventional art, the heat transmitting to the magnet can run away, further, to the housing of the optical pickup, through the metal member for supporting the magnet. Also, within the optical pickup of the thin-type mentioned above, since the metal member for supporting the magnet is exposing outside from the housing of the optical pickup, and further the space around the pickup is narrow within an inside of the thin-type optical disc drive, then it can receive strongly an influence of winds generated by the rotating optical disc, i.e., being high of the capacity of heat radiation, and therefore it is possible to maintain the sufficient performance or capacity the heat radiation, even if the housing of the optical pickup is not made of metal.
However, the mechanism for driving the objective lens, which can be mounted on the optical pickup of thin-type, is restricted in the sizes thereof because it is the thin-type, and is low in the performance or capacity of heat radiation, comparing to that of the objective lens driving mechanism of the large-size optical pickup. Then, for enabling or dealing with high-speed recording onto the optical disc, it is necessary for a drive to have such a disc motor that can rotates the optical disc at high speed, and also to enable to mount the large-size optical pickup thereon, having a high performance mechanism for driving the objective lens.
However, with the large-size optical pickup, it is difficult for heat in the magnet to run into the housing of the optical pickup made of resin, even through the metal members for supporting the magnet. For this reason, there can be considered a problem of lowering of the performances of the magnet due to an increase of temperature of the magnet, and then there appears a necessity for maintaining the performance or capacity of heat radiation, in particular, for the objective lens driving mechanism.
[Patent Document 1] Japanese Patent Laying-Open No. 2001-14712 (2001)